Conventional snow tires provide grip on icy road surfaces via stud pins fitted into the tread portion of the tire.
Typical stud pins are embedded in a stud pin installation hole provided on the tread portion. When stud pins are embedded in a stud pin installation hole, the stud pin installation hole expands in diameter. By inserting stud pins into a stud pin installation hole in this state, the stud pins are firmly embedded in the stud pin installation hole. As a result, stud pins are prevented from falling out from the stud pin installation holes upon receiving forces upon breaking or accelerating or lateral forces from the road surface during rolling motion of the tire.
A spike for a tire (stud pin) that can realize enhanced clawing force against a surface of ice and weight reduction is known (International Patent Publication No. WO/2012/117962). The stud pin is provided with a columnar body to be secured to the tread surface with its one end side in the direction along its central axis fitted into a bottomed hole formed in the tread surface of the tire, and a pin protruding from the other end face of the columnar body in the direction along its central axis. The pin is shaped as an odd-shaped columnar body protruding from the other end face of the columnar body and having recessed portions formed by removing portions straddling the other end face and the peripheral surface of a cylindrical body to extend in the direction along the central axis of the columnar body.
However, snow tires with stud pins travel not only on icy road surfaces, but also on concrete road surfaces and asphalt road surfaces. Concrete road surfaces and asphalt road surfaces are harder than icy road surfaces. On such surfaces, the forces received from the hard road surface cause many stud pins to fall out from the tire when braking, accelerating, or cornering.